I received a suggestion to post a follow-up to my stiffener material
search [260810 MMDigest], so here goes. The suggestions I received
included Formica, red fiber board, balsa wood, Tandy leather bag
stiffener, and 3/32" modeling plywood.

I went to my local crafts and hobby store and found 1/16" modeling
plywood. This matched the thickness of the original stiffeners but
it came in a 3' x 5' sheet, much more than I needed. They also had
1/16" basswood in 4" x 24" planks, which was enough for one set of
stiffeners.

I went with the basswood planks, cut out the stiffener shapes, and
sprayed the tops and sides with two coats of clear lacquer.

Glenn Roat